We asked 6 experts if Donald Trump's unpopularity will doom congressional Republicans

In most years, Ohio Sen. Rob Portman’s reelection bid would look like a sure bet.

Portman is a popular Republican from a state that routinely elects Republicans to Congress. He faces no major scandals, has run a smart and well-funded campaign, and is leading his opponent by more than 5 points in basically every poll.

But this is not a normal year. Donald Trump is getting creamed in Ohio — badly losing the state by about as much as his party’s Senate candidate is winning it. And that gap is raising a critical question: Can Republicans really win Senate races in states where their presidential nominee gets clobbered? Could GOP candidates like Portman really survive amid a Hillary Clinton landslide?

Luckily for us, political scientists have spent years studying the impact of presidential nominees on their party’s state and congressional candidates. I interviewed six of the field’s leading experts to learn more about whether “ticket splitting” — voting for one party’s presidential candidate while also voting for the other party — could bail out the Republicans sinking with the Trumpian ship.

Why ticket splitting is unlikely to save congressional Republicans from a Trump disaster

Once upon a time, it was possible for parties to get their clocks cleaned at the presidential level while also adding to their control of Congress and the statehouses.

Back in the 1960s and ’70s, when the ideological and policy divides between the parties weren’t as large as they are now, ticket splitting was common. Most elections in those decades saw about 30 percent of people vote for one party at the presidential level and a different party down ballot, according to political scientist David Kimball of the University of Missouri St. Louis. In 1984, President Ronald Reagan won a historic landslide while Democrats racked up big gains in the House while also running evenly with the GOP in the Senate.

“You had huge numbers of voters splitting their tickets, with candidates successfully dissociating themselves from their presidential nominees,” says Gary Jacobson, a political scientist at the University of California San Diego. “But that’s changed since then.”

Getty Images

As the parties have gotten more and more polarized, voters have grown less and less likely to vote for both a Democrat and a Republican in the same trip to the polls. In 2012, after years of continual decline, we hit a low point — fewer than 10 percent of voters cast split ballots in the last election, Kimball says.

“The amount of ticket splitting in 2012 was lower than any previous election to the 1920s,” he says.

That was true for both the House and Senate. In 2012, the same party that won a congressional district at the presidential level also lost its House seat in just 6 percent of 435 races — breaking another record going back to the 1920s, according to Kimball.

Over the past few election cycles, in other words, the fates of a party’s presidential candidates and its congressional candidates have become increasingly inseparable. If that holds true in 2016, and if Trump’s polling numbers continue to sink, House and Senate Republicans look to be in terrible shape this November.

The polls suggest congressional Republicans will do okay even if Trump implodes. Are they missing something?

Ralph Freso/Getty Images

The problem with the conclusion that Senate Republicans are screwed by Trump’s implosion is that current polling suggests it’s totally wrong.

Right now, Trump is losing Ohio consistently by about 5 points, just like he’s losing all over the country. But RealClearPolitics shows Portman up by around 6 points in Ohio polling, an 11-point difference.

This trend pops up all over the Senate map. Republicans like New Hampshire’s Kelly Ayotte, Florida’s Marco Rubio, and Pennsylvania’s Pat Toomey are all doing significantly better in their states than their party’s presidential nominee. Iowa’s Republican Sen. Chuck Grassley is running 8 points ahead of Trump in that state.

“Republicans will need lots of ticket splitting to hold on to the House and Senate — and right now the polling is showing a surprising amount of it,” says Barry Burden, a political scientist at the University of Wisconsin.

Republicans have a ton of vulnerable seats to try to defend in 2016, so they’re likely to lose the Senate even if their congressional candidates do significantly better than Trump. But the extent of Republicans’ Senate losses — and, possibly, their control of the House — may depend on the extent to which candidates like Portman and Ayotte can reverse a decades-long decline in ticket splitting.

“This year, the relationship that’s been developing with greater strength over the past decades is getting a direct challenge,” Jacobson says. “In recent elections, ticket splitting has been going away. But in recent elections, we didn’t have Donald Trump.”

The case that Senate Republicans won’t survive a Donald Trump blowout

The political scientists I interviewed all agreed on at least one thing: We don’t really have any idea if a ticket-splitting strategy will work, because we have no recent precedent for what happens when so many candidates run away from their party’s nominee.

(Alex Wong/Getty Images)

But different experts gave different explanations for what might happen in November.

One school of thought is that Senate Republicans won’t be able to escape Trump’s shadow. The argument here is that state polls may show how candidates perform when paired head to head but don’t capture the true dynamics of Election Day — where congressional races tend to get far fewer people to the polls than the much more important presidential race.

“The major factor for who wins is who turns out in the first place. If a lot of people turn out for Trump, they’ll vote Republican; if they’re not voting for president, it’s going to be much harder for the governor and House races,” says Laura Bucci, a political scientist at Indiana State University.

A vanishingly small percentage of voters — about 1 percent — show up because of down-ballot races in presidential years, according to Burden. Without the excitement and high publicity of the presidential race, turnout for midterm elections falls by more than 30 percent. If Republicans are going to rely mostly on down-ballot turnout, their congressional candidates are probably toast — even if they look like they’re ahead in the polls.

“If people on the Republican side are so turned off by Trump that they don’t vote, that’s extremely dangerous to the Republicans in Congress,” says Richard Born, a Vassar College political scientist.

When should moderate Republicans really care to panic about Trump’s sinking numbers?

Just how badly would Trump have to do to throw Democrats both the Senate and the House? In general, it’s hard to know how he’s doing at the House level because polling tends not to get that granular for the presidential race. But Kimball, of the University of Missouri St. Louis, is able to put a number on it.

Bill Clark/Roll Call

He cites the gurus at the Cook Political Report, who have come up with a statistic called the Partisan Voting Index (PVI), which measures a House district’s average vote share for the past two presidential elections.

In prior elections, Kimball notes, House candidates lost 99 percent of the races where their party’s PVI was -6 by 6 percentage points or more. In other words, House Republicans didn’t win seats where Republicans lost at the presidential level by more than 6 points.

“It implies that in a state like Ohio, if Trump loses by more than 6 points, then the GOP Senate candidate in that state will likely lose, too,” he says.

Kimball thinks there’s probably about the same effect at the statewide level. In Ohio, Trump is losing by about 5 points, according to RealClearPolitics’ polling average, which means House candidates there might be fine.

But about 20 House districts are controlled by Republicans where their PVI was only +1 in 2014, according to the Cook Political Report. If a Trump meltdown pushes more and more of those House districts to move into the -6 category, the Republicans’ odds of keeping the House look increasingly unlikely.

This is one reason the margin of a Clinton victory may prove so crucial. In 2012, Mitt Romney lost the presidential election by about 4 percentage points to Barack Obama — which was considered a decisive victory. Clinton these days is generally up around 5 points in the polls, but some have found her leading by as many as 8 or 10 points — a result that would be truly disastrous for Republicans down the ballot.

Why Senate Republicans just might be able to create distance between themselves and Trump

But while Senate Republicans may be banking on a strategy without a recent track record of success, there’s also some reason to think it could work.

The crux of this case rests on the strangeness of Trump.

Ticket splitting has been declining because the parties’ congressional candidates are ever more similar to their presidential nominees. But Trump looks, at least to some observers, very different from the rest of his party. Maybe the congressional Republicans are leading in the polls because voters really do like them more than Trump.

“This election is so all over the place, and Trump doesn’t have a lot of clear policy positions — and when he does, they’re often not with his party,” Bucci says.

Bill Clark/CQ Roll Call/Getty Images

Moreover, some research suggests that voters really do care about ensuring one party doesn’t have too much control. One study, by the University of Michigan’s Walter Mebane, found that around 30 percent of the electorate thinks about balancing power among the branches of government when heading to the polls. (Mebane built what’s called a “rational choice model” of the electorate, using survey data to draw conclusions about voters’ decisions.) That also suggests Portman could benefit from an upsurge of GOP-leaning voters concerned about a Clinton presidency.

“It’s dependent on their policy preferences: If they want a moderate government, and think Clinton is way off to the left, they may use their split ticket to preserve a centrist — or, really, gridlocked — government,” Mebane says. “It’s another way we put pressure against a sweep by one party of all three branches of government.”

Other political scientists have been skeptical of Mebane’s conclusions, saying they think other factors — particularly name recognition and campaign funding — are more likely to be driving ticket splitting. Either way, many Republicans are hoping that whatever once caused voters to recognize the difference between the presidency and Congress will make a roaring comeback in 2016.

“Ticket splitting has been going away. But if it doesn’t come back now, it never will,” Jacobson says.

Watch: How the GOP went from Lincoln to Trump

Will you support Vox today?

We believe that everyone deserves to understand the world that they live in. That kind of knowledge helps create better citizens, neighbors, friends, parents, and stewards of this planet. Producing deeply researched, explanatory journalism takes resources. You can support this mission by making a financial gift to Vox today. Will you join us?

One-Time Monthly Annual

$5/month

$10/month

$25/month

$50/month

Other

$

Yes, I'll give $5/month

Yes, I'll give $5/month

We accept credit card, Apple Pay, and Google Pay. You can also contribute via